This invention relates to a portable hand-held motor driven tool unit and particularly to a small hand-held reciprocating tool adapted to selectively cut, sand or file a relatively stationary work member.
In the construction and forming of various elements, components must be cut and in other instances subject to surface working such as filing, sanding, rubbing or the like. Various specialized tools have been suggested for such system for effecting such working of a member and are advantageously formed to permit interchanging of the tool structures. For example, U.S. Pat. No. 3,240,966 discloses a small electromagnetic portable working tool which was specially designed for receiving various manicuring implements but also notes that it can be applied to other cutting tools such as files and saws as well as impact punches for design, stipling and the like. The structure discloses a battery operated system in which a gear train is coupled to a reciprocating blade support member. The support member projects outwardly of the housing and is adapted to receive a telescoped tool element. A similar device applied to a file structure is also disclosed in a more recent U.S. Pat. No. 4,408,623. In certain cutting equipment such as relatively large portable reciprocating power saws, consideration has been given to the natural balance and unbalanced forces created within the drive system. Thus, for example, U.S. Pat. No. 2,895,514 notes there is unbalance of the dynamic forces between the engine, the saw blade and the interconnecting drive elements. That patent adds a counterbalancing weight structure by using a firing piston which has a weight greater than the combined weight of a blade and a coupling mechanism. The extra weight of the firing piston counterbalances and compensates for the reactive forces created by the cutting action and the reactive force of the accelerating blade and the coupling member. Thus, the total saw mechanism is better balanced in such gas fired system. Considerations are also set forth in U.S Pat. No. 4,699,036 for an electric driven saw cutting mechanism for cutting of a stack of fabric with a mechanism generally known as a trevette or velvet knife. In this structure, an eccentric mechanism is driven to drive a reciprocating cutting blade. The mechanism includes a counterweight driven by a second eccentric oppositely directed to that of the first to compensate for inertia forces generated by the mass of the cutter. This patent also broadly discloses the concept of an external weight releasably mounted to permit the use of different weights for purposes of varying the compensation factor and particularly the turning moment which results from and remains as a result of the use of the two concentric systems. A portable hand held saw with a pair of concentric drives for respectively driving the blade and the counterweight is disclosed in U.S. Pat. No. 2,949,944, which issued Aug. 23, 1960. A saber saw structure employing a counterweighted mechanism is also further disclosed in U.S. Pat. No. 3,942,251, which issued Mar. 9, 1976. These and other patents thus disclose various reciprocating tools, some of which have various means for compensating for the weight and reaction forces within the driving mechanism.
Although various systems have thus considered the problem associated with such tools, there remains a need for a small, inexpensive portable tool particularly adapted for receiving of relatively small filing and cutting tools having means to maintain a very stable system operation.